Flood Frequency Estimates for New England River Restoration Projects: Considering Climate Change in Project Design

Prepared by the NOAA Fisheries Service, this 2011 flood frequency brief and provides guidance for incorporating climate change into river restoration projects. The report explains recent climate and streamflow research, helping river restoration practitioners on improving estimates of flood frequency and magnitude for project design. The document focuses on New England, but is applicable as general guidance for the entire northeastern United States.

The report outlines regional hydroclimatic flood trends for New England watersheds, discussing the effects of watershed land use change and/or flow regulation. Climate change affects flooding through changing magnitude, duration, and timing of streamflow-driving precipitation events. The report cites a study in which 25 of 28 long-term annual flood series showed upward trends in annual flood magnitudes with high significance. The data also showed a step change in 1970 for the region, suggesting a shift in hydroclimate.

Currently, many flood frequency estimates are based upon decades-old Federal Emergency Management Agency (FEMA) Flood Insurance Studies (FISs). The report states these studies are unrepresentative of modern climate effects on flooding, and often are underestimations. In order to more fully account for modern differences in flood trends, such as from climate change and land-use change, the NOAA Restoration Center recommends three major guidelines:

  • basing new frequency estimates on the most recent data available
  • separating pre- and post-1970 records in addition to a full record to select the most conservative (largest) estimates for low-probability events, and
  • considering the use of alternative estimation methods if the flood record does not have recent data. 

 

 

 

Publication Date: 2011

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